[FIX] blockdom: ignore attributes with undefined value

tests/compiler/__snapshots__/attributes.test.ts.snap

@@ -182,6 +182,34 @@ exports[`attributes dynamic formatted attributes with a dash 1`] = `
 }"
 `;
 
+exports[`attributes dynamic undefined class attribute 1`] = `
+"function anonymous(bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, component, comment } = bdom;
+  
+  let block1 = createBlock(\`<div block-attribute-0=\\"class\\"/>\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    let d1 = ctx['c'];
+    return block1([d1]);
+  }
+}"
+`;
+
+exports[`attributes dynamic undefined generic attribute 1`] = `
+"function anonymous(bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, component, comment } = bdom;
+  
+  let block1 = createBlock(\`<div block-attribute-0=\\"thing\\"/>\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    let d1 = ctx['c'];
+    return block1([d1]);
+  }
+}"
+`;
+
 exports[`attributes fixed variable 1`] = `
 "function anonymous(bdom, helpers
 ) {

tests/compiler/attributes.test.ts

@@ -52,6 +52,18 @@ describe("attributes", () => {
     expect(result).toBe(`<div></div>`);
   });
 
+  test("dynamic undefined generic attribute", () => {
+    const template = `<div t-att-thing="c"/>`;
+    const result = renderToString(template, { c: undefined });
+    expect(result).toBe(`<div></div>`);
+  });
+
+  test("dynamic undefined class attribute", () => {
+    const template = `<div t-att-class="c"/>`;
+    const result = renderToString(template, { c: undefined });
+    expect(result).toBe(`<div></div>`);
+  });
+
   test("dynamic attribute with a dash", () => {
     const template = `<div t-att-data-action-id="id"/>`;
     const result = renderToString(template, { id: 32 });